The 64-year-old American pervert, who the FBI said has since killed himself, drugged the youngsters with sleeping pills before pouncing

William Vahey targeted at least 90 children, including Brits, aged 12 to 14 during his sickening spree.

The 64-year-old pervert drugged the youngsters before pouncing.

But police fear the number could be higher as sordid images of his victims found on a memory stick he owned only go back to 2008. It could be the worst ever case of paedophilia involving a teacher.

Vahey worked at the private Southbank International School in London from 2009 to last year and today its chair of governors Sir Chris Woodhead confirmed some of the victims were pupils there.

American national Vahey, who was found dead last month, taught history and geography.

The FBI said Vahey killed himself two days after investigators filed a warrant to search a computer thumb drive belonging to him containing pornographic images of at least 90 boys aged from 12 to 14, who appeared to be drugged and unconscious.

Former Ofsted chief inspector Sir Chris said the independent school was working with the FBI to identify which of the children in the images were from the school.

He said: “Everyone at the school is deeply shocked by what we heard on Tuesday.

“Our two priorities now are to communicate as much information as we have as quickly as we can, and to help the police as much as we can in what is now an international police inquiry into the activities of this man.”

Sir Chris said parents at the school, which teaches pupils aged from three to 18, were very concerned.

He said the fact that Vahey was able to teach there and at other schools despite having a conviction for a child sex offence in California in 1969 “beggars belief”.

But he added that Vahey had an “immaculate record” and had never given any staff at the school any cause for concern.

“He was a very popular man, both with staff and students,” he said. “He has managed to deceive his colleagues in schools all around the world for 30 years."

Sir Chris said that Vahey mainly taught pupils aged between 11 and 14 but also took students out on trips.

Earlier, he told Sky News he felt physically sick when he heard the news, adding: “This is the worst thing that I’ve ever been involved in in 40 years of education.”

Sir Chris said a meeting was due to be held at the school early next week which was due to be attended by police and investigators.

Vahey taught in various international schools, which has led the FBI to believe his victims are from all over the world. Because of the fact that he drugged them, some might not even know they were abused.

It is believed that all of the boys in the images were his students, going back to 2008.

The FBI’s Special Agent Patrick Fransen said: “I’ve never seen another case where an individual may have molested this many children over such a long period of time.

“I’m concerned that he may have preyed on many other students prior to 2008.”

Vahey was confronted about the images by a colleague at the American Nicaraguan School in Managua, Nicaragua, where he had most recently been teaching, and he confessed that he was molested as a child and had preyed on boys all his life, plying them with sleeping pills before abusing them.

The photos were catalogued with dates and locations that corresponded with overnight field trips that Vahey had taken with students since 2008, but he had led pupils on such outings for his entire career.

Vahey, who had a home in London as well as in South Carolina, was found dead in Luverne, Minnesota, on March 21.

Scotland Yard said it was helping the FBI with its inquiries.

A spokesman said: “Officers from the sexual offences, exploitation and child abuse investigation team are assessing and evaluating intelligence passed to the MPS (Metropolitan Police Service) by US authorities, and actively seeking any evidence whilst working with partner agencies to ensure that potential victims are supported.”